1. Field of the Invention
The invention relates in general to an intelligent layer jump method, and more particularly to an intelligent layer jump method applied in optical disc drive.
2. Description of the Related Art
Along with the increasing demand in high-capacity optical recording medium, digital versatile disc (DVD) with more than two recoding layers has gained a great popularity and plays an important role in electronic products. When accessing a DVD disc, the stability and efficiency have become an imminent target for manufacturers in the industry to achieve.
An optical disc drive accesses data by rotating the disc, shifting an optical pick-up head along the radial direction of the disc, and emitting a laser beam onto the recoding layer disposed on the optical disc. Referring to FIG. 1, a sectional view of the conventional dual layer disc is shown. Disc 10 has a first recoding layer 102 and a second recoding layer 104, wherein data are stored between the two recoding layers. In the diagram, two solid arrows 106 and 108 are pointed to a direction departing from the center of the disc, while two solid arrows 110 and 112 are pointed towards the center of the disc. The laser beam is firstly focused on the predetermined recoding layer via an objective lens 114, and then reflected back to the optical detector (not shown in the diagram) of the optical pick-up head.
Referring to FIG. 2, a diagram illustrating the disposition of the optical pick-up head on the optical detector is shown. The optical detector comprises 6 photo-dioxides, wherein the part comprising photo-dioxides 202, 204, 206, 208 can be used to generate a focus error (FE) signal whose intensity is expressed as FE=(A+C)−(B+D), while another two photo-dioxides 210, 212 are the source for generating a tracking error (TE) signal whose intensity is expressed as TE=(F−E).
Referring to FIG. 3A and FIG. 3B; wherein FIG. 3A is a diagram illustrating the cross tracking of the laser beam, while FIG. 3B is a corresponding tracking error signal. When a laser beam 304 shifts upwards, the photo-dioxide 210 receives the light reflected from a track 302, while the photo-dioxide 212 receives a beam of light not reflected from the track 302. Therefore, when the signal received by the photo-dioxide 212 is an intensified signal, the tracking error signal generated is positive (TE=F−E>0), otherwise a negative tracking error signal is generated. If the laser beam is projected on the tracks at the same time, the reflected light received by the photo-dioxide 210 and that received by the photo-dioxide 212 would have the same intensity, meanwhile, the tracking error signal is 0, and each T represents a tracking cross signal period as shown in FIG. 3B.
Currently, DVD disc has several ways to store data therein. For example, a dual disc needs to incorporate the mechanism of layer jump to access data. In FIG. 1, the objective lens 114 is focusing on the recoding layer 102. However, when the optical pick-up head is to access data from the recoding layer 104, the objective lens 114 would be shifted upwardly for the focal point 116 to fall on the recoding layer 104. Contrary, if the optical disc drive needs to turn back to access data from the recoding layer 102, a layer jump would be performed for the focal point 116 to be shifted backwardly to the recoding layer 102 from the recoding layer 104.
However, the eccentricity due to different specifications of discs and spindle motors manufactured by different manufacturers would cause the disc to vibrate and wobble when rotated. And as the rotation rate of the optical disc drive becomes faster and faster, the vibration and wobbling would only get worse not less. Moreover, the outer the tracks on the disc, the worse the wobbling. The layer jump according to prior art directly changes to a target position on another recoding layer from an original position on a recoding layer when the target position is at outer tracks of the disc and the disc is still wobbling. During layer jump, the difficulty in focusing is very likely to cause the focal point 116 to fall on either between the recoding layer 102 and the recoding layer 104 or above the recoding layer 104, thereby ending up with focusing failure. Meanwhile, the focus error signals detected by the optical pick-up head are all equal to 0. Under such circumstances, even focusing compensation technique would not do any good. Moreover, the position of the objective lens 114 after failure in layer jump is normally unknown, so the focusing process has to start from the beginning, which would spend a longer time and result in a poor data accessing efficiency.